why is Flight Gear so slow?

[Douglas Alves]

On Thu, 2005-01-20 at 11:37 -0500, Will Backman wrote:

> Run (from the terminal) glxgears and xdpyinfo.
> 
> glxgears will tell you your frame rate.  If you have proper hardware
> accelerated OpenGL, you should get frame rates in the thousands, and
> only in the hundreds if you are using software OpenGL.

1) On starting glxgears it spat this error first:
   Xlib:  extension "XFree86-DRI" missing on display ":0.0".

   Am I missing an upgrade or what?

2) glxgears reports 130 FPS if I'm not doing anything else. But what
should I look for in xdpyinfo ?
  Would selecting a screen mode of 800x600 improve things?